Diesel fuel stabiliser

ABSTRACT

There is provided use of a thermal stabiliser for increasing the thermal stability of a cetane improver in a fuel composition comprising (i) a fuel, and (ii) the cetane improver wherein the thermal stabiliser is a compound of the formula 
     H—R 1   
     wherein H is a group comprising a heterocyclic group and R 1  is a hydrocarbyl group having from 10 to 200 carbons.

[0001] The present invention relates to a diesel fuel stabiliser. In particular the present invention relates to a stabiliser for a diesel fuel containing a cetane improver.

[0002] As discussed in U.S. Pat. No. 5,482,518 fuel ignition in diesel engines is achieved through the heat generated by air compression, as a piston in the cylinder moves to reduce the cylinder volume during the compression stroke, In the engine, the air is first compressed, then the fuel is injected into the cylinder; as the fuel contacts the heated air, it vaporises and finally begins to bum as the self-ignition temperature is reached. Additional fuel is injected during the compression stroke and the fuel burns almost instantaneously, once the initial flame has been established. Thus, a period of time elapses between the beginning of fuel injection and the appearance of a flame in the cylinder. This period is commonly called “ignition delay” and must be relatively short in order to avoid “diesel knock”.

[0003] A major contributing factor to diesel fuel performance and the avoidance of “diesel knock” is the cetane number of the diesel fuel. Diesel fuels of higher cetane number exhibit a shorter ignition delay than do diesel fuels of a lower cetane number. Therefore, higher cetane number diesel fuels are desirable to avoid diesel knock. Most diesel fuels possess cetane numbers in the range of about 40 to 55 and a sulfur content of about 500 ppm and less. A correlation between ignition delay and cetane number has been reported in “How Do Diesel Fuel Ignition Improvers Work” Clothier, et al., Chem. Soc. Rev, 1993, pg. 101-108.

[0004] Cetane improvers have been used for many years to improve the ignition quality of diesel fuels. The use of cetane improvers is increasing due to the increased demand for diesel fuel which has resulted in a widening of the fraction recovered, the so called middle distillate fraction, and the lower natural cetane number of diesel base stocks caused by more severe refining of crude oil and the effort made to produce low emission diesel.

[0005] Many types of additives have been prepared and evaluated to raise the cetane number of diesel fuel. Such additives include peroxides, nitrates, nitrites, azo compounds and the like.

[0006] Alkyl nitrates such as amyl nitrate, hexyl nitrate and mixed octyl nitrates have been used commercially with good results. Other nitrates such as 2-methyl-2-nitropropyl nitrate (U.S. Pat. No. 4,536,190) have been suggested as cetane improvers but found shock sensitive, However, it is generally accepted that organic nitrates, more specifically the commercial 2-ethylhexyl nitrate, are the most cost-effective additives to improve cetane number of diesels. 2-ethylhexyl nitrate is available from the Associated Octel Company Limited under the brand name Cl-0801.

[0007] It is known that 2-ethylhexyl nitrate (2-EHN) has a de-stabilising effect on many diesel fuels when subjected to high temperature test conditions, such as ASTM D6468-99, Standard Test Method for High Temperature Stability of Distillate fuels. D6468 is a test that involves aging fuel for 90 or 180 minutes at a temperature of 150° C. This is a temperature above the auto-decomposition temperature of cetane improvers such as 2-EHN, and the decomposition products promote instability of diesel fuels.

[0008] Recent data by Bacha, et al. have demonstrated that high temperature stability as measured in D6468 is related to on-road performance of diesel trucks. Because of these findings, the National Council of Weights and Measures has chosen to specify test results developed from ASTM D6468 as a partial basis for defining “premium” diesel fuel in the United States. There is therefore a desire to overcome the problems of diesel destabilisation by cetane improvers, in particular by 2-EHN.

[0009] The prior art has provided some additives which are normally used to improve storage stability and will give some improvement in ASTM D6468. EP-A-0947577 teaches tertiary alkyl primary amines may stabilise diesel fuel containing cetane number improver.

[0010] The present invention alleviates the problems of the prior art

[0011] In a one aspect the present invention provides use of a thermal stabiliser for increasing the thermal stability of a cetane improver in a fuel composition comprising (i) a fuel, and (ii) the cetane improver, wherein the thermal stabiliser is a compound of the formula H—R¹ wherein H is a group comprising a heterocyclic group and R¹ is a hydrocarbyl group having from 10 to 200 carbons.

[0012] In a further aspect the present invention provides a fuel composition comprising (i) a fuel (ii) a cetane improver (iii) a thermal stabiliser, wherein the thermal stabiliser is a compound of the formula H—R¹ wherein H is a group comprising a heterocyclic group and R¹ is a hydrocarbyl group having from 10 to 200 carbon.

[0013] The present inventors have found that compounds such as those defined in the present claims, for example polyisobutenyl succinimide (PIBSI), are surprisingly effective in stabilising cetane improvers in diesel fuel. In particular the present compounds are effective in reducing the thermal degradation of cetane improvers such as 2-EHN.

[0014] The present inventors have found and have demonstrated in the attached examples that the present thermal stabilisers such as PIBSI effectively stabilise cetane improvers in diesel and in some aspects are provide improved stabilisation when compared to the istabilisers of the prior art, for example the stabilisers of EP-A-0947577.

[0015] Furthermore, in aspects of the invention, for example when PIBSI is used as a stabiliser, the thermal stabiliser has a further functionality—it is an effective detergent to improve injector cleanliness, for example in an L-10 Cummins diesel engine (a test is commonly used in the USA) and other diesel engine detergency tests.

FURTHER ASPECTS

[0016] In the present specification by the term “hydrocarbyl group” it is meant a group comprising at least C and H and may optionally comprise one or more other suitable substituents. Examples of such substituents may include halo-, alkoxy-, nitro-, a hydrocarbon group, an N-acyl group, a cyclic group etc. In addition to the possibility of the substituents being a cyclic group, a combination of substituents may form a cyclic group. If the hydrocarbyl group comprises more than one C then those carbons need not necessarily be linked to each other. For example, at least two of the carbons may be linked via a suitable element or group. Thus, the hydrocarbyl group may contain hetero atoms. Suitable hetero atoms will be apparent to those skilled in the art and include, for instance, sulphur, nitrogen and oxygen.

[0017] Thermal Stabiliser

[0018] R1 Group

[0019] Preferably R¹ is a branched or straight chain alkyl group. Preferably R¹ is a branched alkyl group.

[0020] R¹ may be a C₁₀-C₂₀₀ hydrocarbon group. R₁ is preferably a C₃₀-C₈₀ group and more preferably a polyisobutene (PIB).

[0021] Conventional PIBs and so-called “high-reactivity” PIBs (see for example EP-A-0 565 285) are suitable for use in the invention. High reactivity in this context is defined as a PIB wherein at least 50%, preferably 70% or more, of the terminal olefinic double bonds are of the vinylidene type, for example the GLISSOPAL compounds available from BASF.

[0022] Preferably R¹ has a molecular weight of from 200 to 2000, more preferably 260 to 1000, for example about 260, 320, 350, 550, 750, 780 or 1000, more preferably from 750 to 780.

[0023] Preferably R¹ is a PIB having a molecular weight of from 200 to 2000, more preferably 260 to 1000, for example about 260, 320, 350, 550, 750, 780 or 1000, more preferably from 750 to 780.

[0024] H—Heterocyclic Group

[0025] Preferably the heterocyclic group is a hydrocarbyl ring at least one member of which is selected from N, S and O. The ring portion of such a ring is referred to as a heterocyclic ring. Preferably at least one member of the hydrocarbyl ring is N.

[0026] Preferably the heterocyclic ring has from 4 to 10 members, more preferably from 4 to 6 members, yet more preferably 5 members.

[0027] Preferably the heterocyclic ring is substituted. Preferably the heterocyclic ring is substituted with one or more=O groups.

[0028] Preferably the heterocyclic ring is of the formula

[0029] R² may be selected from hydrogen, C1-20 straight, branched or substituted alkyl, or polyamine. The alkyl may be methyl, ethyl, butyl. The polyamine may be ethylenediamine, diethylenetriamine, triethylenetetraamine, tetraethylenepentaamine, pentaethylenehexamine, dimethylaminopropylamine, aminoethylethanolamine, and other commercially available materials which comprise complex mixtures of polyamines.

[0030] Preferably the heterocyclic group comprises linker via which the heterocyclic ring is attached to R¹. Preferably the linker group is a C₁₋₅ alkyl group, more preferably a C₁₋₃ alkyl group, yet more preferably a —CH₂— group.

[0031] Preferably N—R² is a residue of a long chain polyalkylenepolyamine.

[0032] Stabiliser H—R¹

[0033] The compound H—R¹ may in the form of a “dimer” or may capped with a further H group. Thus in one aspect the compound H—R¹ may be present in the form of a compound of the formula H—R¹—R¹—H or H—R¹—H. In further aspects, the thermal stabilser

[0034] Preferably the thermal stabiliser is polyisobutene succinimide monotetraethylene pentaamine. More preferably the thermal stabiliser is polyisobutene succinimide monotetraethylene pentaamine having a PIB molecular weight of from 200 to 2000, more preferably 260 to 1000, for example about 260, 320, 350, 550, 750, 780 or 1000, more preferably from 750 to 780. In a highly preferred embodiment the thermal stabiliser is 780-polyisobutene succinimide monotetraethylene pentaamine.

[0035] Cetane Improver

[0036] Preferably the cetane improver is 2-ethylhexyl nitrate.

[0037] Fuel

[0038] Preferably the fuel is a diesel fuel

[0039] Composition

[0040] The thermal stabiliser compound of the present invention can be combined with other additives to give other improvements, in an additive package/thermal stabiliser composition. The thermal stabiliser composition may comprise, in addition to the thermal stabiliser, antihaze additives, 2-EHN, corrosion inhibitors, lubricity improvers, cold flow improvers, or icing inhibitors.

[0041] In one aspect the thermal stabiliser composition may comprise a mixture of compounds of the formula H—R¹, H—R¹—R¹—H and/or H—R¹—H. In this aspect, preferably the R¹:H ratio in the composition is 1-1.5:1 or 1-1.2:1 or approximately 1:1

[0042] The present invention will now be described in further detail in the following examples.

EXAMPLES

[0043] In the attached examples and tabulated data, a reflection rating is obtained from a filter paper after aged fuel is filtered under standard conditions. The reflection rating is a relative indication of the amount of sediment formed in the fuel after aging at 150° C. A rating of 100 is the highest rating and shows that no sediment was formed under the test conditions. High reflection values (80-100) indicate satisfactory fuel. Values less than 80 have decreasing stability, and values under 50 can be considered poor.

Example 1

[0044] A number of tests were performed. In each test a fuel composition containing (i) low Sulphur Diesel, (ii) 2-EHN and (iii) additive was aged in accordance with D6468 at 150° C. for 180 minutes All samples contained 0.15 volume percent 2-EHN. Data in Table 1 shows results for a number of thermal stabilisers. These are FOA-81- 780 - polyisobutene succinimide monotetraethylene pentaamine (−60%), Shellsol AB (−40%) + dehazer (<2%) FOA-3- N,N-dimethylcyclohexylamine FOA-6- organic amines in kerosene solvent FOA-5- methacrylate polymer in xylene FOA-15- methacrylate polymer, FOA3, metal deactivator + corrosion inhibitor FOA-35A- FOA3, FOA5, metal deactivator + corrosion inhibitor Nalco 5300 - organic amine stabiliser

[0045] Each of FOA-3, FOA-6, FOA-5, FOA-15, FOA-35A, and Nalco 5300 are premier stabilising additives to improve stability of diesel fuels. Each of FOA-3, FOA-6, FOA-5, FOA-15, and FOA-35A are available from Associated Octel Company Limited. Nalco 5300 is available from Nalco Chemical Company. TABLE I Additive D1500 Color % Reflection Sample ID Type Conc. Ptb Initial Final Y green filter P97-1297 None — L1.5 5.0 42 N5300 10 L5.0 43 20 L5.0 46 FOA-5 10 L6.0 46 20 L6.5 53 FOA-6 10 L5.0 56 FOA-81 15 L6.5 77 30 L6.0 89 FOA-15 25 L6.0 66 FOA-35A 25 L6.0 69 P98-1025 None — L1.5 L5.5 23 N5300 10 L5.5 33 20 L4.5 36 FOA-5 10 L5.5 34 20 L6.0 36 FOA-6 10 L5.0 31 FOA-81 15 L5.5 74 30 L6.5 88 FOA-15 25 L5.5 68 FOA-35A 25 6.0 68 P97-942 None — L1.5 L3.0 91 N5300 10 L3.0 92 20 L2.5 91 FOA-5 10 L3.0 95 20 L3.0 95 FOA-6 10 L2.5 93 FOA-81 15 L2.5 98 30 L2.5 98 FOA-15 25 L3.0 97 FOA-35A 25 L2.5 98 P97-296A None — L0.5 L4.5 50 N5300 10 L5.0 47 20 L4.5 52 FOA-5 10 L5.0 42 20 L6.0 48 FOA-6 10 L5.0 55 FOA-81 15 L6.0 67 30 L5.0 88 FOA-15 25 L4.0 81 FOA-35A 25 L5.0 85

[0046] These data show that FOA-81 (shown in bold in the table) is far more effective in improving the filter reflection rating than the other materials tested

Example 2

[0047] A number of tests were performed. In test related to a low sulphur diesel fuel. Samples comprised (i) base fuel containing no cetane improver or thermal stabiliser—control, (ii) base fuel and 2-EHN, and (iii) base fuel, 2-EHN and given additive. When present, 2-EHN was supplied by Associated Octel Company Limited under the brand name Cl-0801 and was present in an amount of 0.15 volume percent.

[0048] Data in Table 2 shows results for a number of thermal stabilisers. These are

[0049] FOA-81-780-polyisobutene succinimide monotetraethylene pentaamine

[0050] Primene 81-R-tertiary alkyl primary amine of the formula (C₁₂₋₁₄)₃CNH₂

[0051] Primene JM-T-tertiary alkyl primary amine of the formula (C₁₆₋₂₂)₃CNH₂

[0052] Primene 81-R and Primene JM-T are available from Rohm and Haas. TABLE 2 Additive D1500 Colour % Reflection Fuel ID Type Conc. ptb Initial Final Y P99-262 Control 0 L1.5 L3.0 82 (CI-0801 only) 0 L7.5 38 FOA-81 + 30 L7.0 78 CI-0801 Primerie 81-R + 30 L4.5 36 CI-0801 Primeno JM-T + 30 L5.5 56 CI-0801 P99-575 Control 0 L1.0 L2.5 88 (CI-0801 only) 0 L6.0 47 FOA-81 + 10 L4.5 90 CI-0801 Primene 81-R + 10 L5.0 62 CI-0801 Primene JM-T + 10 L5.0 56 CI-0801 P99-643 Control 0 L1.5 L2.5 92 (CI-0801 only) 0 L5.5 54 FOA-81 + 10 L4.5 80 CI-0801 Primene 81-R + 10 L5.0 67 CI-0801 Primene JM-T + 10 L5.0 76 CI-0801 P99-644 Control 0 L1.5 L2.5 83 (CI-0801 only) 0 L5.5 70 FOA-81 + 10 5.5 92 CI-0801 Primene 81-R + 10 L4.5 86 CI-0801 Primene JM-T + 10 L5.0 83 CI-0801

[0053] These data show that FOA-81 (shown in bold in the table) is far more effective in improving the filter reflection rating than the other materials tested

[0054] All publications mentioned in the above specification are herein incorporated by reference. Various modifications and variations of the described methods and system of the invention will be apparent to those skilled in the art without departing from the scope and spirit of the invention. Although the invention has been described in connection with specific preferred embodiments, it should be understood that the invention as claimed should not be unduly limited to such specific embodiments. Indeed, various modifications of the described modes for carrying out the invention which are obvious to those skilled in chemistry or related fields are intended to be within the scope of the following claims. 

1. Use of a thermal stabiliser for increasing the thermal stability of a cetane improver in a fuel composition comprising (i) a fuel, and (ii) the cetane improver wherein the thermal stabiliser is a compound of the formula H—R¹ wherein H is a group comprising a heterocyclic group and R¹ is a hydrocarbyl group having from 10 to 200 carbons.
 2. A fuel composition comprising (i) a fuel (ii) a cetane improver (iii) a thermal stabiliser, wherein the thermal stabiliser is a compound of the formula H—R¹ wherein H is a group comprising a heterocyclic group and R¹ is a hydrocarbyl group having from 10 to 200 carbon.
 3. The invention of claim 1 wherein the fuel is a diesel fuel
 4. The invention of claim 1, 2 or 3 wherein the cetane improver is 2-ethylhexyl nitrate.
 5. The invention of claim 1, 2, 3 or 4 wherein R¹ is a branched or straight chain alkyl group.
 6. The invention of claim 5 wherein R¹ is a branched alkyl group.
 7. The invention of claim 5 or 6 wherein R¹ is polyisobutene.
 8. The invention of any one of the preceding claims wherein R¹ has a molecular weight of from 750 to
 780. 9. The invention of claim 5 or 6 wherein R¹ is polyisobutene having a molecular weight of from 750 to
 780. 10. The invention of any one of the preceding claims wherein the heterocyclic group is a hydrocarbyl ring at least one member of which is selected from N, S and O.
 11. The invention of claim 10 wherein at least one member of the hydrocarbyl ring is N.
 12. The invention of claim 10 or 11 wherein the heterocyclic ring has from 4 to 10 members.
 13. The invention of claim 12 wherein the heterocyclic ring has from 4 to 6 members.
 14. The invention of claim 13 wherein the heterocyclic ring has 5 members.
 15. The invention of any one of claims 10 to 14 wherein the heterocyclic ring is substituted.
 16. The invention of claim 15 wherein the heterocyclic ring is substituted with one or more=O groups.
 17. The invention of any one of claims 10 to 16 wherein the heterocyclic ring is of the formula


18. The invention of any one of claims 10 to 17 wherein the heterocyclic group comprises linker via which the heterocyclic ring is attached to R¹.
 19. The invention of claim 18 wherein the linker group is a C₁₋₆ alkyl group.
 20. The invention of claim 19 wherein the linker group is a C₁₋₃ alkyl group.
 21. The invention of claim 20 wherein the linker group is a —CH₂— group.
 22. The invention of any one of the preceding claims wherein the compound H—R¹ is present in the form of a compound of the formula H—R¹—R¹—H.
 23. The invention of any one of the preceding claims further comprising a compound of the formula H—R¹—H.
 24. The invention of claim 23 wherein the R¹:H ratio in the composition is 1-1.5:1 or 1-1.2:1 or approximately 1:1
 25. The invention of any one of claims 17 to 24 wherein N—R2 is a residue of a long chain polyalkylenepolyamine.
 26. The invention of any one of the preceding claims wherein the thermal stabiliser is 780-polyisobutene succinimide monotetraethylene pentaamine.
 27. A use as substantially herein before described with reference to any one of the Examples.
 28. A fuel composition as substantially herein before described with reference to any one of the Examples. 